As the so-far known practical methods of reducing carbonyl compounds, there may be mentioned Meerwein-Ponndorf-Varley reduction (MPV reduction), the reduction using diisobutylaluminum hydride (DIBAH) and so on.
The MPV reduction is a method of reducing carbonyl compounds using an aluminum trialkoxide, such as Al(OiPr).sub.3, as a reducing agent or a reducing catalyst. This method is in frequent use as an economical method of reducing various ketones and aldehydes, since aluminum trialkoxide used there and alcohol such as isopropanol are inexpensive (Organic Reactions, volume 2, page 178 (1944)).
The technologies for asymmetric reduction of carbonyl compounds using MPV reduction can include, for example, the known method which uses aluminum as a center metal of a catalyst and uses an optically active alcohol as a chiral resource as well as a hydrogen transfer resource; however, its optical purity generally tends to be low and the chiral resource needed is theoretically in an equimolecular amount or more to the substrate (Asymmetric Organic Reactions, Prentice-Hall Inc. (1971)).
As examples of other technologies for asymmetric reduction, there can be exemplified the asymmetric reduction by (-)-isoborneol using a porphyrin complex with aluminum as a catalyst (Journal of Organic Chemistry, volume 55, page 816 (1990)), and the asymmetric reduction by isopropanol using a complex of an optically active alcohol with lanthanoid (Journal of American Chemical Society, volume 15, page 9800, (1993)). Said technologies, however, have problems that the chiral resources and the metal catalysts are expensive.